A sperm donor in Kansas is fighting attempts to force him to pay child support for a baby conceived with a lesbian couple.

William Marotta from Topeka donated sperm to Angela Bauer and Jennifer Schreiner in 2009, after answering an ad on online bulletin board Craigslist.

The 46-year-old took no money for the donation and signed away all parental rights, including financial responsibility to the child.

But when the women filed for state assistance in Kansas this year, the state demanded to know the biological father's name so it could collect child support for the now three-year-old girl.

The state contends the agreement between Mr Marotta and the women is not valid because Kansas law requires a licenced physician to perform the artificial insemination.

"If a sperm donor makes his contribution through a licenced physician and a child is conceived, the donor is held harmless under state statue," argued Angela de Rocha, a spokeswoman for the Kansas Department for Children and Families.

"In cases where the parties do not go through a physician or a clinic, there remains the question of who actually is the father of a child or children."

Ms Bauer and Ms Schreiner - who have since separated - have said they fully support Mr Marotta's efforts to fight the state's request.

Mr Marotta has said he does not resent the couple for revealing his identity.

"I resent the fact that Jennifer was pressured into doing that in the first place," he said. "That was wrong - wrong by the state."

Mr Marotta told The Topeka Capital-Journal newspaper he's "a little scared about where this is going to go, primarily for financial reasons."

"I've already paid more than 10% of my yearly salary, and I don't know many folks who are willing to give up more than 10% of their yearly income," he said.

A hearing on a motion by his lawyer to dismiss the case is scheduled for January 8.